Although the present invention is generally applicable to probing any device, the present invention is particularly suited for probing an integrated circuit to test the circuit. As is known, integrated circuits are typically manufactured as a plurality of dies on a semiconductor wafer. FIG. 1 illustrates a typical test system 100 for testing such a semiconductor wafer 124. The exemplary test system shown in FIG. 1, includes a tester 102, a test head 118, a probe card 106, and a prober 120.
A semiconductor wafer 124 is placed on a chuck (also commonly referred to as a stage) 114, which typically is capable of movement in the “x,” “y,” and “z” directions. The chuck 114 may also be capable of being rotated (e.g., in the “θ” direction) and tilted and may be further capable of other motions as well. Once the semiconductor wafer 124 is placed on the chuck 114, the chuck is typically moved in the “x,” “y,” and/or “θ” directions so that terminals on the dies (not shown) of the wafer 124 align with probes 108 on the probe card 106. The chuck 114 then typically moves the wafer 124 upward in the “z” direction, bringing the terminals into contact with the probes 108. One or more cameras 122 may aid in aligning the terminals and the probes and determining contact between the probes 108 and the terminals.
Once the terminals of the dies (not shown) are in contact with the probes 108, a tester 102, which may be a computer, generates test data. The test data is communicated through one or more communication links 104 to a test head 118. The test data is communicated from the test head 118 through interconnections 116 (e.g., pogo pins) to the probe card 106 and finally to the terminals of the dies (not shown) through probes 108. Response data generated by the dies are communicated in reverse direction from the probes 108, through the probe card 106, through interconnections 116, through the probe head 118, through a communication link 104, to the tester 102.
FIGS. 2A-2C illustrate movement of the wafer 124 into contact with the probe card 106. As mentioned above and shown in FIG. 2A, terminals 220 of one or more dies 202a of wafer 124 are aligned with probes 108 of the probe card 106. The chuck 114 them moves the wafer upward such that the terminals 220 of the die 202a contact probes 108, as shown in FIG. 2B. As shown in FIG. 2C, the chuck 114 typically moves the wafer 124 beyond first contact with the terminals 220. (Movement beyond first contact is often referred to as “over travel.”) This typically compresses the probes 108. The resulting spring force exerted by the probes 108 against the terminals 220 helps to create a reasonably low resistance electrical connection between the probes and the terminals. In addition, the probes 108 often wipe across the surface of the terminals 220 as the probes are being compressed. The wiping action tends to cause the tips of the probes 108 to break through any oxide or other build up on the terminals 220, again helping to create a reasonably low resistance electrical connection between the probes and the terminals.
As might be expected, compression of the probe 108 and the wiping action induce forces and stresses in the probe, which may break, damage, or reduce the useful life of a probe 108. In addition, the force exerted by the probe 108 against the terminal 220 may damage the terminal 220 and/or the wafer 124. A wafer 124 comprising material with a low “k” dielectric may be particularly susceptible to such damage. Generally speaking, the greater the friction between a probe 108 and a terminal 220, the greater such forces and stresses are likely to be. Indeed, it is possible for frictional forces to prematurely stop the wiping of the probe 108 tip across the terminal 220. This may happen, for example, if the probe 108 tip digs too deeply into the terminal 220 or if the probe tip gets caught in an irregularity on the surface of the terminal. If the probe 108 tip stops its wiping motion prematurely, the forces and stresses that build up on the probe may become particularly large (and therefore particularly likely to cause damage to the probe, terminal, and/or wafer). Although a probe 108 may dig into any type of terminal 204, a probe 108 is particularly susceptible to digging into a terminal made of a soft material (e.g., solder ball or aluminum terminals) or a terminal with a rough surface (e.g., copper terminals). Embodiments of the present invention, among other things, may reduce stresses in a probe and forces exerted by and against a probe. One nonlimiting advantage of the invention is in reducing or replacing the vertical component of relative movement between the probe and the terminal as they are brought into contact by a wiping action, which reduces the forces on and stresses in the probe.